This application relates generally to disc drives and more particularly to an improvement in a disc drive actuator assemblies and voice coil motors. More specifically, the invention relates to an actuator body that uses a stiffener member that is overmolded with the voice coil motor, as well as a process for manufacturing the actuator assembly.
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on a disc. Modern disc drives comprise one or more rigid discs that are typically coated with a magnetizable medium and mounted on the hub of a spin motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by transducers (xe2x80x9cheadsxe2x80x9d) mounted to an actuator assembly for movement of the heads relative to the discs. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment.
The heads are each mounted via flexures at the ends of actuator arms that project radially outward from the actuator body or xe2x80x9cExe2x80x9d block. The actuator body typically pivots about a shaft mounted to the disc drive housing adjacent the outer extreme of the discs. The pivot shaft is parallel to the axis of rotation of the spin motor and the discs, so that the heads move in a plane parallel to the surfaces of the discs.
Typically, such actuator assemblies employ a voice coil motor to position the heads with respect to the disc surfaces. The voice coil motor typically includes a flat coil mounted horizontally on the side of the actuator body opposite the actuator arms. The coil is immersed in a vertical magnetic field of a magnetic circuit comprising one or more permanent magnets and vertically spaced apart magnetically permeable pole pieces. When controlled direct current (DC) is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the voice coil moves, the actuator body pivots about the pivot portion and the heads move across the disc surfaces. The actuator assembly thus allows the head to move back and forth in an accurate fashion between an inner radius and an outer radius of the discs.
Critical to these operations is the accurate controlled movement of the recording head to and from desired data tracks and precision track following. It is essential that the actuator system be free of low frequency, high amplitude resonances. One common resonance inherent to all rotary actuators is a mode in which the voice coil tends to bend laterally about the pivot shaft due to the actuator body""s mass moment and its relatively high inertia. This resonance affects the accuracy of head positioning, and therefore limits track density, an important problem in disc drie design. Currently, the voice coil is held in place using a plastic overmold material attached to the pivot portion of the actuator body for ease in design and manufacturing. However, the use of plastic is not always advantageous because it is structurally weak and it contributes to undesirable resonances.
Earlier actuator designs included a pair radially spaced aluminum fingers added to the actuator body radiating from the pivot portion. The voice coil was held in place between the fingers using an adhesive. However, adhesives, such as epoxy, are expensive and cause undesirable outgassing within the drive. The current, conventional overmold techniques and material eliminates epoxy and provides additional benefits of being able to incorporate complex latching and servo track features into the actuator design. The disadvantage is that the overmold introduces undesirable resonances as described above.
Accordingly there is a need for an actuator assembly that achieves the benefits of the overmolding techniques while at the same time minimizing undesirable resonances.
Against this backdrop the present invention has been developed. The present invention is an actuator assembly that includes an actuator body with stiffening members that are embedded within an overmold that attaches the voice coil motor armature to the pivot portion of the actuator body. Preferably a pair of spaced stiffening members extend from the pivot portion of the actuator body in a direction generally opposite of the actuator arm portion. The voice coil is carried between the stiffening members by enclosing the stiffening members and the voice coil.
The stiffening member in the overmold enhances the rigidity of the actuator body interface, minimizing low frequency, high amplitude resonances during drive operations. Additionally, by improving the rigidity of the actuator body and the voice coil motor armature, the accuracy of positioning the heads at the distal ends of the actuator arms is improved permitting narrower track spacing and thus greater opportunity for increasing track density on data storage discs.
The material and method used for the overmold is generally, but not limited to, plastic that is injection molded. The use of overmolds and stiffening members also maintains the benefits of reduced weight and thermal expansion of the voice coil motor armature portion.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.